This application relates to systems and methods for removing and trapping sediment entrained in moving water so that the sediment does not enter and pollute the local streams and rivers network. Such systems are typically called “check dams” or sediment barriers. More specifically, the invention relates to biodegradable modular structures from which sediment barrier structures may be constructed.
It is very common to see bare soil slopes and drainage waterways near highways and constructions sites. When water flows quickly over exposed soil waterways and down slopes before vegetation covers the bare soil, the flow erodes the soil and carries the eroded soil and deposits the soil as sediment in surrounding natural waterways. If these sediments were not removed before they reached the natural waterways, they would pollute those waterways. Therefore, effective sediment control has become a major task in construction sites. To protect natural watersheds from polluting sediment, regulatory agencies like the U.S. Environmental Protection Agency have toughened regulations and strictly enforced those regulations, which has added to the demand for sediment control devices.
Various types of sediment control devices are now available. However, conventional sediment barriers do not perform well on all three factors. Conventional devices for controlling erosion and sediment on construction sites include sediment barriers made of hay bales, silt fences, rocks, stuffed fiber rolls, and a silt barrier with a triangular cross section (e.g., U.S. Pat. No. 5,605,416). These dams are placed at regular intervals in drainage ditches and on slopes to reduce the velocity of the water flowing over and through them and remove sediment entrained in the water.
The effectiveness of a sediment barrier structure is determined by, among other factors, its ability to: (1) remove a large percentage of sediment from water flowing through and/or over the dam, (2) accumulate a large volume of sediment before its ability to remove sediment degrades, and (3) become quickly integrated into the environment without interfering with the natural processes of the ecosystem in which it is installed. Efficiency, eco-friendliness, and cost are important factors to consider when selecting sediment control devices. Efficiency of a sediment control device relates to how well it blocks or traps sediment while allowing sediment free water to pass through and to the length of its functional life. Failure to account for functional life of a sediment control device could lead to serious problems during its applications.
Conventional sediment barriers do not perform well on all three factors. For example, sediment barriers made using fabric silt fences clog easily. The water flows through the fabric in the direction approximately perpendicular to the fabric surface and sediment collects in the fabric. Because the fabric is thin, it has little capacity to hold sediment before the spaces between fibers in the fabric becomes clogged.
In addition it is not that easy to remove a sediment barrier once sediment is deposited on it. Rock sediment barriers do not promote vegetation and they look very ugly in the middle of a waterway or on a slope in which vegetation has started to grow. Rock dams are also very hard to maintain since rocks tend to move when subjected to heavy flow conditions.
Dams made using hay bales or stuffed fiber rolls sometimes permit water to flow under the dam structure, which is sometimes called “under cutting.” Under cutting compromises the effectiveness of the dam because the water flowing under the dam erodes the soil under the dam and creates an unimpeded flow path. If the erosion caused by under cutting is severe, the velocity and volume of water flowing under the dam may cause the dam to fail.
Additionally, many conventional sediment barriers do not promote the growth of vegetation on and/or near the installation site. Because conventional dams either completely block the flow of water through them or quickly clog with sediment, a “pond” forms behind the dam soon after it is installed. The water in the pond impedes growth of most vegetation in the soil covered by the pond. Moreover, as rain and other sources of water flow into the pond at varying rates, the size of the pond behind a conventional dam changes. As the pond covers more soil, it may kill vegetation that had previously started growing on “dry” soil. A long dry spell can let the pond drain and allow vegetation to grow. However, if a new pond forms, the vegetation may die. Therefore, conventional sediment barriers typically impede growth of vegetation in the area behind the dam.
Virtually all sediment barriers in the form of continuous barriers and diversion dikes are quickly buried under the accumulated sediment that they remove from passing water. Whenever a buried sediment barrier is made of materials that are not 100 percent biodegradable, the dam must be removed soon after the dam stops removing sediment. Removing sediment barriers is labor intensive and expensive and disturbs the soil. Disturbing the soil increases the risk that erosion will recur at the site from which the dam was removed. Moreover, sediment-clogged sediment barriers are typically disposed of landfills, which consumes increasingly scarce landfill space.